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Abstract

We present several applications of microstructured optical fibers and study their modal characteristics by using Bragg gratings inscribed into photosensitive core regions designed into the air-silica microstructure. The unique characteristics revealed in these studies enable a number of functionalities including tunability and enhanced nonlinearity that provide a platform for fiber device applications. We discuss experimental and numerical tools that allow characterization of the modes of the fibers.

(a) Typical transmission spectrum of FBG in standard fibers exhibiting short wavelength loss. Each dip in the transmission spectrum is associated with grating facilitated phase matching to a counter-propagating cladding mode. The inset shows a schematic of Bragg grating in the core of a conventional optical fiber. Fig. 3. (b) The corresponding transmission spectrum of LPG.

Experimental setup used to characterize near field images for respective air-silica MOFs. Bragg grating selectively excited counter-propagating “cladding modes” which are imaged in the near field on the VIDECON camera.

(a) Part of transmission spectrum of FBG written into the core of the grapefruit MOF (solid line) with the corresponding observed near field images of light reflected off FBG when the laser was tuned to (A) 1553.96nm (the LP01 mode); (B) 1552.39nm (LP 02); (C) 1550.84nm (LP03) mode; (D) 1547.82nm (LP04 mode); (E) 1547.36nm (LP05 mode); (F) 1535.82nm, and (b) calculated modal spectrum of the grapefruit MOF (dashed line) and its corresponding simulated modes.

(a) Schemaitc drawing of material (polymer) infused in the air-holes of the MOF. (b) Picture showing material in the air-holes of the fiber. (c) Refractive indices of the polymer and silica dependence on temperature.

Index cross-sectional profile in the waist of the fiber (a) with no polymer and with polymer of index (b) lower (np=1.42), (c) same as (np=1.44) and (d) higher (np=1.5) than that of silica. The corresponding calculated intensity cross sectional mode profile are shown at (1) z=0 cm, (2) z=1cm and (3) z=2 cm along the length of the waist.